1. Field of the Invention
The invention relates in general to an emission material, and more particularly to a phosphorescent emission material and the organic electroluminescent device using the same.
2. Description of the Related Art
In recent years, organic electroluminescent display has gained a rapid growth, and transition metal complex compounds are widely applied to the emission material. Take the emission layer for example, the emission material is categorized as fluorescent type and phosphorescent type. The luminous efficiency of the phosphorescent type is about three times as higher as that of the fluorescent type. The phosphorescence normally exists in the form of transition metal complex compounds. Due to the heavy-atom effect, intersystem crossing would occur, triplet excitation state is formed, the occurrence of phosphorescence is increased, and the fluorescent intensity is weakened. Therefore, the development of a phosphorescent material with high efficient is critical to increase the luminance efficiency of the entire device.
The recent development in the phosphorescent material is focused on transition metal complex compound. In prior art and related patents, the central metal of phosphorescent material is focused on transition metal with d6 configuration such as platinum (Pt), osmium (Os), iridium (Ir), rhenium (Re) and ruthenium (Ru). Iridium metal, having the features of stronger bonding with ligand, long-lived excitation state and higher luminous efficiency, is conventionally used as the central metal of phosphorescent material. In recent years, the development of the blue phosphorescent material is focused on iridium metal complex compound, and iridium (III)bis(4,6-di-fluolophenyl)-pyridinato-N,C2′) picolinate (Flrpic) blue phosphorescent material is the most popular one.
The Flrpic blue phosphorescent material is poor in sublimation, so temperature control during the purification process becomes a critical factor. Moreover, the temperature of the Flrpic blue phosphorescent material during the sublimation and purification process is hard to control, so that the Flrpic blue phosphorescent material is decomposed during the sublimation and purification process, causing the yield rate of the Flrpic blue phosphorescent material to decrease.
It can be seen from prior art and related patents that the maximum wavelength of emission (λmax) of the Flrpic blue phosphorescent material in solution state is 476,492 (nm), the maximum wavelength of emission of the device using the Flrpic blue phosphorescent material is 475,498 (nm), and the CIE[x, y] value of the device is [0.16, 0.29]. Therefore, the photochromism of the Flrpic blue phosphorescent material and the device using the same is not blue enough.